Question

Which of the following is a reason for conjugating proteins? To direct their delivery to a particular organelle To direct their delivery to the cell membrane To add a cofactor needed for their activity (A) I only (B) II only (C) II and III only (D) I, II, and III

Short answer

The correct answer is (D) I, II, and III.

Step-by-step solution

Understand the Question

Determine what 'conjugating proteins' means and identify why this process is used in cellular biology.

Analyze each statement

Evaluate statements I, II, and III to determine if they are valid reasons for conjugating proteins.

Evaluate Statement I

Statement I: 'To direct their delivery to a particular organelle.' This is correct as conjugation helps target proteins to specific cellular locations.

Evaluate Statement II

Statement II: 'To direct their delivery to the cell membrane.' This is also correct; certain proteins must be directed to the cell membrane.

Evaluate Statement III

Statement III: 'To add a cofactor needed for their activity.' This is correct as well; conjugation can add necessary cofactors to proteins.

Choose the Correct Answer

Since statements I, II, and III are all valid reasons for conjugating proteins, the correct answer is (D) I, II, and III.

Key concepts

Cellular Biology

Cellular biology, also known as cell biology, involves the study of cells and their physiological properties, structures, organelles, interactions, and the life cycle. Understanding cellular biology is essential as it provides the foundation for comprehending more complex biological systems.

Every cell consists of various organelles, each performing specific functions to maintain cell viability. For instance, mitochondria generate energy, while the Golgi apparatus modifies and sorts proteins. Knowing how proteins interact within these organelles helps us understand cellular processes and functionality.

Proteins play a critical role in cellular biology as they are involved in virtually all cell functions. They act as enzymes catalyzing biochemical reactions, structural components providing support, and signaling molecules facilitating communication within and between cells.

Protein Targeting

Protein targeting is the process by which proteins are directed to specific locations within or outside the cell. Once synthesized, proteins need to reach their correct destinations to perform their functions properly. This is where conjugation comes into play.

Conjugating proteins means attaching certain molecules or tags to proteins, which act like 'addresses' that help direct them to the right cellular locations. For example:

• Proteins destined for the cell membrane might get lipid modifications.
• Proteins meant for the nucleus might have nuclear localization signals (NLS).

Protein conjugation ensures that proteins are efficiently delivered to where they are needed, which is crucial for maintaining cellular order and functionality. Mis-targeted proteins can lead to diseases or cellular malfunctions.

Cofactors

Cofactors are non-protein chemical compounds that are required for the biological activity of proteins, typically enzymes. They can be metal ions like zinc or magnesium, or organic molecules such as vitamins.

Cofactors are essential because they help enzymes catalyze reactions by stabilizing their active sites or participating in the enzyme's chemical reaction. Without the appropriate cofactor, an enzyme might be inactive or less efficient.

When a protein is conjugated with a cofactor, it ensures that the protein is fully functional and capable of performing its biological role. For example:

• Hemoglobin requires iron as a cofactor to transport oxygen.
• Enzyme carbonic anhydrase needs zinc to catalyze the conversion of carbon dioxide to bicarbonate.

Hence, protein conjugation to include necessary cofactors is a critical aspect of cellular functionality and enzyme activity.